The long-term goal of the proposed research plan is to identify the roles which different sensory inputs play and the operations performed by central neural structures in mediating some of the reflex behaviors which contribute to the control of vertical gaze and head posture. In particular the research is directed toward the following objectives: (a) to characterize the interaction among vestibular, visual and neck proprioceptive inputs vis a vis the motor outputs, (b) to define the specific operations performed by the cerebellum and brain stem structures in mediating the reflex behaviors, and (c) to understand the pathophysiology underlying disorders of gaze and postural equilibrium and to identify adaptive strategies used by the central nervous system in compensating for vestibular deficits. The more specific aims of this proposal deal with the vertical semicircular canal and otolith interactions which are mediated by the interstitial nucleus of Cajal and related structures. Behavioral observations and quantitative analyses of input-output relations will serve to define the dynamic characteristics. Selective lesions of neuron populations by a neurotoxic agent and single unit recordings will provide some insight into the actual pathways and mechanisms involved.